A polycarbonate resin has a high refractive index and excellent transparency and impact resistance and is now widely used as a raw material for lenses, especially spectacle lenses. Since polycarbonate resin spectacle lenses are thinner and lighter than conventional glass lenses and plastic lenses formed by cast polymerization (to be referred to as “cast lenses” hereinafter), have extremely high impact strength and are therefore safe and highly functional, they are used as visual correction lenses, sunglasses and protective spectacles.
It is now strongly demanded that eyes should be protected from harmful ultraviolet rays by providing ultraviolet absorptivity to spectacle lenses. A coating layer having ultraviolet absorptivity is formed on the surface of a cast lens or glass lens to meet the above demand. However, the lenses obtained by the above coating method become expensive and yellowish. An ultraviolet absorbing agent is added before polymerization to manufacture a cast lens. However, the above method has problems such as the hindrance of polymerizability and the marked yellowing of the lens itself.
In contrast to this, in a polycarbonate resin spectacle lens, the polycarbonate resin itself has a certain measure of ultraviolet absorptivity on a short wavelength side, and ultraviolet absorptivity can be easily provided to the polycarbonate resin by adding an ultraviolet light absorber before melt-molding as it is a thermoplastic resin. Therefore, the addition of an ultraviolet light absorber having a long wavelength is proposed. However, a polycarbonate resin of the prior art can absorb ultraviolet radiation having a wavelength of up to 375 nm. To absorb ultraviolet radiation having a wavelength longer than this, the amount of the ultraviolet light absorber must be added in an amount 2 to 10 times larger than that of the prior art. Since the ultraviolet light absorber is generally sublimable, when a large amount of the ultraviolet light absorber is added, the ultraviolet light absorber sublimes and contaminates the mirror surface of a mold at the time of injection molding the polycarbonate resin and the appearance of the obtained lens is greatly impaired.
JP-B 06-035141 and JP-B 06-041162 disclose a method of forming a surface layer at the time of extrusion molding a multi-layer sheet or film by adding 0.1 to 20 parts by weight of an oligomer type ultraviolet light absorber which hardly sublimes in a polycarbonate resin. However, the purpose of this method is to provide weatherability to the sheet and not optical. There is an ultraviolet light absorber which can absorb ultraviolet radiation having a longer wavelength. Since the polycarbonate resin yellows markedly when this long wavelength absorbing ultraviolet light absorber is added, a large amount of a bluing agent must be added to remove the yellow color. However, as transparency is impaired and luminous transmittance is greatly reduced by the addition of the large amount of the bluing agent, a lens having a markedly dark color is provided.
Further, JP-A 07-092301 proposes a plastic lens which prevents the transmission of ultraviolet radiation and near infrared radiation by adding an ultraviolet light absorber and an infrared light absorber. However, the lens obtained by this method is unsatisfactory in terms of transparency.
Meanwhile, JP-A 62-146951 discloses a polycarbonate resin composition which is prepared by adding 0.001 to 5 parts by weight of an alkylidene bis(benzotriazolylphenol) compound represented by a specific structural formula to 100 parts by weight of a polycarbonate resin to improve light resistance. This publication shows the measurement results of a change (ΔYI) in the yellowness index of each test specimen which was prepared by adding 0.30 wt % of each of the above five specific compounds to a polycarbonate resin and applying ultraviolet radiation to the test specimen from a high-pressure mercury lamp to measure the yellowness index of the specimen. The results merely show that a change in the yellowness index is reduced by the addition of the above specific compounds.
JP-A 04-292661 discloses a resin composition comprising 100 parts by weight of a transparent thermoplastic resin including a polycarbonate resin and 0.01 to 0.15 part by weight of an ultraviolet light absorber having an absorption maximum at a wavelength of 280 to 360 nm and no absorption at a wavelength of 400 nm. This resin composition has been developed for camera lenses having a transmittance for light having a wavelength of 400 nm of 80% or more as the sensitivity peak of a silver salt film is existent at a wavelength of 400 nm.
JP-A 09-263694 and JP-A 09-291205 disclose a resin composition comprising 100 parts by weight of a transparent thermoplastic resin including a polycarbonate resin and two ultraviolet light absorbers having absorption maximums at a wavelength of 300 to 345 nm and a wavelength of 346 to 400 nm. Although this composition has been developed for spectacle lenses having excellent transparency and high ultraviolet absorptivity, when heat history such as re-extrusion is applied to recycle product waste, a change in hue is large and molding heat resistance is unsatisfactory.
Further, JP-A 2003-231803, JP-A 2003-231804 and JP-A 2003-231805 disclose a resin composition comprising 100 parts by weight of an aromatic polycarbonate resin and 0.003 to 1 part by weight of a specific benzotriazole-based ultraviolet light absorber and a benzofurano-2-one type compound. Although this composition has improved balance among hydrolytic resistance, impact resistance and mold contamination, it is unsatisfactory in terms of hue and when heat history such as re-extrusion is applied, a change in hue is large and molding heat resistance is unsatisfactory.
The pamphlet of WO03/095557 discloses a composition comprising (a) a polycarbonate resin, (b) a specific full ester of an aliphatic polyhydric alcohol and an aliphatic carboxylic acid and (c) an ultraviolet light absorber. The polycarbonate resin composition disclosed by this document is unsatisfactory in terms of ultraviolet absorptivity required for spectacles lenses.
When a molded product is taken out from the mold, smooth releasability that prevents a scratch on the surface of a molded product is required as the quality of a spectacle lens. When a large amount of a release agent is added, adhesion between the molded product and a protective coat for preventing a scratch on the surface of the molded product becomes low due to the influence of the release agent remaining on the surface of the molded product, whereby the protective coat readily peels off. Therefore, a release agent which provides a release effect with a small amount is desired.